How do I seed a random class to avoid getting duplicate random values

Question

I have the following code inside a static method in a static class   Random r   new Random    int randomNumber   r Next 1 100     I have this inside a loop and I keep getting the same randomNumber   Any suggestions here

User · Answer

Bit late  but the implementation used by System Random is Environment TickCount   public Random        this Environment TickCount        This avoids having to cast DateTime UtcNow Ticks from a long  which is risky anyway as it doesn t represent ticks since system start  but  the number of 100-nanosecond intervals that have elapsed since 12 00 00 midnight  January 1  0001  0 00 00 UTC on January 1  0001  in the Gregorian calendar     Was looking for a good integer seed for the TestApi s StringFactory GenerateRandomString

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I use this for most situations  keep the seed if there is a need to repeat the sequence      var seed    int  DateTime Now Ticks      var random   new Random seed     or      var random   new Random  int DateTime Now Ticks

User · Answer

You should not create a new Random instance in a loop  Try something like   var rnd   new Random    for int i   0  i  lt  100    i      Console WriteLine rnd Next 1  100      The sequence of random numbers generated by a single Random instance is supposed to be uniformly distributed  By creating a new Random instance for every random number in quick successions  you are likely to seed them with identical values and have them generate identical random numbers  Of course  in this case  the generated sequence will be far from uniform distribution   For the sake of completeness  if you really need to reseed a Random  you ll create a new instance of Random with the new seed   rnd   new Random newSeed

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this workes for me   private int GetaRandom                 Thread Sleep 1           return new Random DateTime Now Millisecond  Next

User · Answer

public static Random rand   new Random       this happens once  and will be great at preventing duplicates   Note  this is not to be used for cryptographic purposes

User · Answer

In case you can t for some reason use the same Random again and again  try initializing it with something that changes all the time  like the time itself   new Random new System DateTime   Millisecond  Next      Remember this is bad practice though   EDIT  The default constructor already takes its seed from the clock  and probably better than we would  Quoting from MSDN       Random     Initializes a new instance of the Random class  using a time-dependent default seed value    The code below is probably your best option    new Random   Next

User · Answer

A good seed initialisation can be done like this  Random rnd   new Random  int DateTime Now Ticks     The ticks will be unique and the cast into a int with probably a loose of value will be OK

User · Answer

A good seed generation for me is   Random rand   new Random Guid NewGuid   GetHashCode       It is very random  The seed is always different because the seed is also random generated

[c#] How do I seed a random class to avoid getting duplicate random values

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